If I saw this picture with no caption, I’d know I was seeing dwarf galaxies colliding; the shape and the glow from newly-forming stars is a dead giveaway. But I’d also guess that the galaxies were young; old galaxies tend not to have much gas in them, and there’s clearly plenty of that in those galaxies! But in fact the galaxies here are very old; there are globular clusters (spherical collections of perhaps a million stars each that tend to orbit outside of galaxies) in the group that can be dated to being 10 or so billion years old. That means these are old objects, reinvigorated by their collision.

In fact, star clusters inside the galaxies can be dated as well, and appear to be only a few million years old. Oddly, the gas content of the galaxies is very high, with about five times as much as the Milky Way has. That’s pretty weird; it should’ve been used up a long time ago. Apparently, these galaxies have lived very sedate lives until very recently. I’ll note that they are relatively close to us, about 166 million light years away. Usually, colliding dwarf galaxies like this are seen billions of light years away, so we really are seeing them as they appeared recently.

Apparently, the lower-case g-shaped object on the left is the result of two galaxies smashing into each other, and the longer galaxy above them is separate. The spiral to the right is part of this as well and may be involved in the gravitational dance; you can see a splotchy arm of material pointing right at it from the collision on the left. Typically in collisions the gravity of one galaxy draws matter out of the other, and that can collapse to form stars. The red glow is from gas excited by newly born stars, and the blue glow is from these stars themselves. The galaxies are pouring out ultraviolet light (the purple glow) which is another dead giveaway of vigorous star formation.

The background galaxies are gorgeous, too. There’s a phenomenal distant open spiral on the bottom, to the left of center, and what looks like yet another pair of interacting galaxies at the bottom left, obviously much farther away than the Hickson group. Take a minute to look around the high-res version to see what else you might find!

Yup. I guess you can teach old galaxies new tricks… and even sometimes jaded astronomers, too.

I’d like to have a closer look at that orange blob sitting just above the colliding galaxies in the lower left-hand corner. Its features are not as crisp as many of the other background galaxies, but it does appear to have an arm of sorts pointing to the upper left, as well as a bulge on the center right. Perhaps a product of more colliding galaxies?

EDIT: Also, at this resolution it appears to only (or mostly) emit infrared (orange). I’m guessing that two galaxies fairly depleted of their gas and/or colliding in such a way could account for the apparent lack of new star formation. Yea? Nay?

I have several questions about view like this. Example: Does “our” galaxy look like the one on the upper left when viewed from the right distance/angle? If so, why isn’t there tons more apparent light in our neighborhood?

Does “our” galaxy look like the one on the upper left when viewed from the right distance/angle?

Not sure but it woulddepend on how loosely you translate the word “like” perhaps. Our galaxy does have a bit of awarp and is a large-ish bnarred spiral galaxy if thathelps any. That galaxy seen edge on is probably more spiral and more warped although its a bit hard to tell from that perspective.

If so, why isn’t there tons more apparent light in our neighborhood?

Its a *very* big neighbourhood is why!

Also they may have more galaxies & more closely packed together in that galaxy cluster than in our Local Group of galaxies which has just three reasonably large spirals – Andromeda, the Milky Way and M33 the Triangulum or Pinwheel Galaxy.

I’m not 100% sure but I think that mostly explains it although your question also evokes Olber’s Paradox of “why is the sky dark” which you may benefit from researching if you haven’t already.

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